Accurate and repeatable pressure measurements are an important requirement for the operation of both industrial and research vacuum systems. Pressure gauge sensors used to measure vacuum levels in such applications operate based on a wide range of technological principles and share common building blocks in their design, including: (1) a leak tight envelope that houses the pressure sensing elements, (2) electrical feedthroughs that bridge the envelope walls and exchange power, bias voltages and measurement signals with the electronics and (3) a flange that allows leak tight connection of the gauge sensor to the vacuum system port. Historically, pressure gauge sensors have relied on well-established design and manufacturing methodologies that use metallic materials and ceramic insulators. Legacy gauge construction materials are the result of the natural evolution of vacuum technology research and satisfy the mechanical, electrical and high vacuum compatibility properties that are expected from vacuum pressure sensors.
Ionization vacuum gauges are well known and include both hot and cold cathode gauges. A cold cathode ionization gauge has a pair of electrodes (i.e., an anode pin and a cathode cage) in an evacuated envelope which is connected to the vacuum to be measured. In the cold cathode gauge, a high DC voltage potential difference is applied between the anode electrode and the cathode electrode to cause a discharge current to flow therebetween. A magnetic field is applied along the axis of the electrodes in order to help maintain the discharge current at an equilibrium value which is a repeatable function of pressure. Cold cathode ionization gauges are used to measure pressures extending from medium to high vacuum levels (e.g., in the range of 1E-10 to 1E-02 Torr).
Accordingly, an ionization vacuum gauge provides an indirect measurement of vacuum system total pressure by first ionizing gas molecules and atoms inside its vacuum gauge envelope and then measuring the resulting ion current. The measured ion current is directly related to the gas density and gas total pressure inside the gauge envelope, i.e., as the pressure inside the vacuum system decreases, the measured ion current decreases. Gas specific calibration curves provide the ability to calculate total pressures based on ion current measurements.